{ Some car manufacturers do not recommend boosting a vehicle, They state that damage to electronic controls can occur if voltage surges flow through the electrical system during boosting. Instead of boosting, the auto manufacturers prefer that a fully charged battery be installed in place of the dead one or that the dead battery be charged. This is often impractical because of where the vehicle is sitting so most people with a dead battery boost their vehicle - but several important steps must be followed to prevent damage. } Come 'on... is it impossible to throw in some protection electronics? And what about this surge?...Wimpy car electronics? Perhaps HV spikes from the booster wire inductance can zap the computer and other loads.. Would you buy a car that has a big sticker: "Contains sensitive electronics..do not boost"
There's a bit of a contradiction in this article. Reading further down, we find:
"On many new vehicles, the battery is concealed under the rear seat, in the trunk or beneath plastic covers in the engine compartment. Fortunately, the manufacturers usually provide a positive connector under the hood to provide a connection point for boosting. Look for it under a bright red plastic cap marked 'battery' or with a + sign."
If the manufacturers provide a means of boosting the battery, they are saying it won't damage the car (when done properly.)
Most tow trucks will boost a battery with no hesitation. A few simple precautions helps avoid problems, like turning the ignition off on the car before connecting the cables.
Once the cables are connected, it's difficult to see how a surge could produce voltages high enough to destroy any electronics. The two batteries in parallel would absorb the surge.
In cold weaather, it's important to keep a discharged battery from freezing. This means getting it recharged, or removing it and taking it inside to keep it warm.
Eventually the battery will fail to hold a charge, and the only solution is to get a new one. If it's more than three years old, I'd replace it before bad weather starts.
---- mmmm... agencies defining voltages (>>12V) as a result of load dump..SGS doing similiar. It's evidence of overvoltage.
High currents + inductance = spiker? Somewhere I'm guessing. But..it's a battery to battery circuit as one poster pointed out. Isn't that dead battery a dead end? Kinda like creating a surge past a parallel capacitor.
Without studying lead acid battery behavior...maybe a dead lead battery is at it's highest internal impedance. I'm guessing that first crappy connection with the gater clips pulses anything heavy with inductance which spikes the auto electronics. Dunno...
I wonder if there's a product out there.. call it.."Booster Saver" :) that claims to protect the auto electronics during a boost. $$$$ :) D _---------------
I guess what might happen is you get a load dump when you take the cables off, if the battery is still dead. You could use some kind of snubber to prevent this, I guess, but if it means an extra clip on the booster nobody's going to use it.
Andy answers: If the dead battery is completely dead, it will not provide a stabilizer to the system. Assuming the jumper cables can start the dead car, when the jumper cables are removed, the alternator in the dead car will not be stabilized by the battery, and the output voltage will run high. Some of the electronics in the dead car may not be protected against this high voltage.
Note that ALL automobiles have manuals that warn the operator to NEVER disconnect the battery with the engine running. That is exactly the same problem as stated above.... It has nothing whatever to do with the charging vehicle.
The storage battery is the primary voltage stabilizing device in an alternator-battery system. It must be in good shape for the electrical system to work as designed.....
Transients on the vehicle battery line can be a real pain for the designer.
Load dump, as has been discussed, is normally the result of the battery being disconnected while the alternator is at full charge. The alternator generates a huge electrical transient as a result of the "increased" load impedance. This transient is seen all over the vehicle battery harness.
Most modern alternators are "centrally suppressed", in that they incorporate a local zener to eat the overvoltage. Hence, the maximum load dump is clamped at the source.
Some alternators are not centrally suppressed. Then the transient is eaten by all the boxes on the harness. (or maybe the one with the least series inductance, from the alternator). In any event, every box usually has to be designed to eat the entire energy slug. Number and location of such boxes vary from vehicle to vehicle.
These transients are not for sissies. A 12V system might be 70V through 4 ohms. A 24V system might be 150V through 0.75 ohms. Further, the spec might require a repetitive pulse for an extended period of time.
The designer is forced to follow one of two paths:
1) Insure all circuits can handle the overvoltage.
2) Clamp it with a TVS
Solution 1 is the simplest. However, this means all MOSFETS might be
100V (or greater) - with increased RDSon. Hence they dissipate more power under nominal conditions. Further, this decreased efficiency is a real bummer with the controller in a 125`C environment. This means larger packages, more substantial thermal designs, larger footprint, etc. Any DC/DC converters must be able to maintain its V(o) of ~5V under this transient. That's a Vin range of 4.5V (crank) to ~100V(load dump).
Solution 2 is sometimes better. However, the TVS clamp cannot commence until just above jump start voltage (typically 2x nominal). Further, the worst case tolerance on the TVS might mean one can't start clamping until ~40V for a 12V system. So, all MOSFETS are 50V - with their reduced efficiency. The issue worsens at 24V when the jump start is
48V (or higher) and the currents are much more substantial.
Back to OP's comment..... I s'ppose the real risk is to the jumper's car rather than the jumpee's car. His car is seeing the most substantial impedance transient. The jumpee benefits from the load of the dead battery. This is speculation on my part.
Cars are no longer dominated by mechanical systems - electronics is a very major part.
users will connect devices up backwards, discharge freakish ammounts of electrosytatic charge into sensitive electrics and do other unfortunate things, manufacturers are covering their assets.
correct usage of booster cables isn't simply a matter of matching positive and negative on both sides
Nah. The alternator is the primary voltage stabilizing device in the system. It sets the voltage to around 14.5V, depending on temperature.
I have had plenty of occasions where I left the lights on or had some other problem that drained the battery completely.
A discharged battery still has a specific gravity of around 1.130, meaning it has plenty of sulfuric acid remaining. This means it will have a low resistance. This will prevent the alternator from developing a high output voltage.
When you boost the battery, you have one car with the engine running, and one car cranking. The source alternator is putting out as much current as it can, and the target battery is receiving some charge.
When the target engine starts, its alternator starts developing current to charge the battery. Now you let the throttle off the source engine so it goes to idle, and remove the jumper cables.
Since the target battery is taking most of the current from the alternator, there is no large reduction when the cables are removed, so there is no load dump from the alternator.
The load dump occurs when there is a high current drain and the battery is disconnected. That never happens during a boost, so there is little cause for concern.
Just watch the tow trucks during a cold spell. They pop the cables on, get the engine started, remove the cables, and get the owner to sign the bill. Then they're on their way to the next poor victim.
About the only reason for a problem is poor connections to the battery. If they suddenly open while the alternator is delivering high current, it will cause a load dump and fry the electronics.
This could happen while removing the jumper cables, and people would think it was caused by the boost.
That proportional spacing is a pain in the ass. I have vision problems, and it is very hard to read with my vision problems. Its one of the reasons I had to stop reading the local newspaper. I learned to speed read 40 years ago, but it only works on properly laid out text.
"Pretty print" is a waste of time and energy, not to mention that it takes longer to upload and download the files. You might as well be using HTML with 6 pt type and a different color on every character.
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ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=148254 . A relatively safe way to boost is to turn off the "dead" car's ignition. Then connect the boost cables. Do not attempt to start the "dead" car with the boost cables connected. Let the Booster car charge the dead battery to the point where it is capable of starting the car. This will take several minutes. Remove the boost cables. Start the "dead" car using its own recharged battery.
Yes, but I don't know what it's called - maybe "jump start battery"....
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is one example.
It's just a portable starting battery, about the size of a thick telephone book. I think it'd be safe to just clip that across the battery. I had that done once, and I was amazed at how "well" the car cranked - it seemed like the jumper battery didn't even droop at all. :-)
The jump cables have finite resistance, and are not disconnected until the jumpee's car is running (so voltage has equalised somewhat) add to that that the jumper typically has a better battery than the jumpee and that it's fully charged.
Normally the battery will swallow any surges from the altenator that are due to changing load.
One should always check to make sure there is no open cell/circuit in the current battery that is mounted in the car otherwise, a boost start will most likely cause damage as soon as you remove the external source from it's own source.. Most of the time you should first clean your connector clamps before jumping since, this maybe the original reason why your battery is low/dead in the first place. If you do have a bad connection at the cables and you boost start, your electrical system may become unstable because the alternator is not seeing a constant voltage at it's output terminal which causes it's own regulator to become unstable since it treats the battery as if it was a capacitor also. Many car's employ protection in this area, for example, if you get a boost start and if the battery is completely shot or cable/clamps have no connection, as soon as you disconnect the boost cables, the car will stall.
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Some more items in the equation: More modern cars have more never off electronics Alarms, keyless entry systems, etc., There is an additional hazard in Jumping a car, "polarity reversal". very little auto electronics is well protected for this.
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JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.
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This is the big danger in boosting with someone who does not know what they are doing. When a battery is dead, is it very easy to do a polarity reversal.
I was doing just this one time, and the guy had no clue, and he started to clip the cables onto his battery backwards. I said, "NONONONONONONO!!!!!!", and luckily he stopped in time.
I 'splained to him, and said, "I didn't really know what to say..." and he said, "Well, 'NONONONONONONO!!!!!!' seems to've worked pretty good." :-)
On most cars the first sign that you've reversed the cables is smoke coming from the alternator. The diodes in there keep the battery from back-discharging into the stator windows. Reverse the jumper cables and you have a few hundred amps going thru some #12 wires, which don't take long to burn up.
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